1. Field of the Invention
The present invention relates to a deodorant and a process for deodorization using said deodorant. More particularly, the present invention relates to a deodorant which can efficiently remove smell caused by hydrogen sulfide or mercaptans with use in a small amount and a process for deodorization which enables rapidly and efficiently removing smell caused by hydrogen sulfide or mercaptans in waste water, sludge formed in treatments of waste water, such as raw sludge, excess sludge, digested sludge, and flocculated sludge, water discharged from washing apparatuses, and mixtures of these substances with use of the above deodorant in a small amount.
2. Description of the Related Arts Recent concentration of population to urban and suburban areas leads to consumption of a large amount of water. After being used in such areas, the water resources become waste water containing various organic and inorganic substances, which is discharged into public sewer systems or pits in buildings. In the process of treatment of waste water in sewage treatment plants, large amounts of raw sludge, excess sludge, and digested sludge are formed. In business plants, such as large manufacturing plants, regulations on waste water have been made stricter after occurrence of serious environmental pollution in rivers and seas, and treatments of waste water are enforced to achieve the specified quality of waster water. A large amount of sludge is formed in the precipitation treatment with flocculation or the treatment with active sludge in business plants.
Such waste water and sludge contain sulfates and large amounts of components causing buildup of BOD (biological oxygen demand). In waste water and sludge, sulfate reduction bacteria are generally present and conduct production activities, reducing sulfates in the sludge to hydrogen sulfide. The formed hydrogen sulfide is discharged into the gas phase because hydrogen sulfide is a gas at a room temperature. Hydrogen sulfide is toxic and has unpleasant smell. Leak of hydrogen sulfide from manholes of the sewer system or from underground of buildings causes the problem of smell to residents in the area. Moreover, there is the possibility of danger to workers during treatments of sludges. Hydrogen sulfide is oxidized by sulfate oxidization bacteria attached to facilities of concrete and the air and dissolved into mist to form sulfuric acid. Sulfuric acid thus formed corrodes concrete which is alkaline and metal to cause fatal defects to the structure of buildings. Mercaptans are formed in the process of putrefaction of waste water and sludge in a manner similar to the formation of hydrogen sulfide to cause the problem of smell.
To prevent generation of smell and corrosion of structures, pH may be adjusted to an alkaline condition using sodium hydroxide or the like to suppress vaporization of hydrogen sulfide. However, hydrogen sulfide itself is not decomposed or removed in accordance with this process. Hydrogen sulfide is generated again or alkali scales are formed when the treated water is neutralized. Therefore, this process is not satisfactory. As another process, hydrogen peroxide may be added to oxidize components causing smell. This process has a problem that, when hydrogen peroxide is used in a small amount, hydrogen sulfide is formed again from products of the oxidation, such as sulfur or sulfate ion, by the action of bacteria after sludge is left standing for a long time although hydrogen sulfide and mercaptans can be removed once. As another process, a metal salt may be added to fix hydrogen sulfide as a salt of the metal. In this process, hydrogen sulfide is fixed as a metal sulfide by the reaction of the metal ion and hydrogen sulfide, but this process has a problem that a large amount of sludge is formed.
Waste water or sludge may be treated with active charcoal to adsorb hydrogen sulfide. In this process, however, the used active charcoal must be regenerated or replaced with fresh active charcoal when the adsorption is saturated, and this causes economic disadvantage because replacing active charcoals requires an additional operation and the cost of regeneration is, high.
Alternatively, smell may be removed by passing waste water or sludge through a biological phase which is supported on a support and packed. However, this process has problems that a large apparatus is necessary and that maintenance and control of the biological phase is not easy. Generation of hydrogen sulfide may be suppressed by addition of a salt of nitric acid into waste water. However, the salt of nitric acid itself cannot oxidize sulfides.
Under the above circumstances, the first object of the present invention is to provide a deodorant which can efficiently remove smell caused by hydrogen sulfide or mercaptans with use in a small amount.
The second object of the present invention is to provide a process for deodorization which enables rapidly and efficiently removing smell caused by hydrogen sulfide or mercaptans in waste water, sludge formed in treatments of waste water, such as raw sludge, excess sludge, digested sludge, and flocculated sludge, water discharged from washing apparatuses, and mixtures of these substances with use of a deodorant in a small amount.
As the result of extensive studies by the present inventors to achieved the above objects, it was found that the first object can be achieved by a deodorant comprising a combination of a peroxide and a nitrate ion, a combination of a peroxide, a nitrate ion, and a metal salt, or a combination of a chelating agent and one of the above combinations. It was also found that the second object can be achieved by a process comprising treating a substance for treatment containing hydrogen sulfide or mercaptans with the above deodorant.
The present invention has been completed on the basis of the above knowledge.
Accordingly, the present invention provides:
(1) A deodorant for substances containing hydrogen sulfide and/or mercaptans which comprises a combination of a peroxide and a nitrate ion (referred to as deodorant 1, hereinafter);
(2) A deodorant for substances containing hydrogen sulfide and/or mercaptans which comprises a combination of a peroxide, a nitrate ion, and a metal salt (referred to as deodorant 2, hereinafter);
(3) A process for deodorization comprising treating a substance for treatment containing at least one compound selected from the group consisting of hydrogen sulfide and mercaptans with a deodorant described in (1) (referred to as process for deodorization 1, hereinafter); and
(4) A process for deodorization comprising treating a substance for treatment containing at least one compound selected from the group consisting of hydrogen sulfide and mercaptans with a deodorant described in (2) (referred to as process for deodorization 2, hereinafter).